High-frequency pulse generator



J. A. RADO HIGH-FREQUENCY PULSE GENERATOR Oct. 22, 1946;

Filed Feb. 27, 1945 FIG.2

INVENTOR. JOHN A. RADO 45 1i ATTORNEY Patented Oct. 22, 1946 HIGH-FREQUENCY PULSE GENERATOR John A. Rado, Little Neck, N. Y.," assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application February 27, 1945, Serial No. 579,955

The present invention is directed to high-frequency pulse generators of the type in which pulses are generated in response to the periodic charging and discharging of an energy-storage device. While the invention is subject to a variety of applications, it is especially suited to generator arrangements in which the energystorage device is charged and discharged through gasdilled electron-discharge devices and will be particularly described in that connection.

As utilized throughout the present description and in the appended claims, the expression highfrequency pulse generator is intended to designate a generator for producing output pulses which may occur at high repetition frequencies.

A high-frequency pulse generator of the type under consideration i disclosed in copending application, Serial No. 579,954, filed February 2'7, 1945, in the name of John A. Rado and assigned to the same assignee as the present invention. In that arrangement, a transmission-line section is utilized as an energy-storage device, being charged from a potential source through a vacuum tube and thereafter being discharged rapidly through a gas-filled tube. A pulse transformer coupled into the discharge circuit of the line section supplies an output pulse of a given polarity to a load circuit upon each discharging of the line. Such an arrangement has very desirable operating characteristics. For example, the generated pulses have a substantially rectangular wave form and a duration approximately equal to 2\ LC, where L and C, respectively, designate the total inductance and total capacitance of the transmission line. Also, pulses of high peak power may be generated while thearrangement operates at moderate supply voltages, thus obviating the necessity for an elaborate highvoltage power supply and reducing the equipment cost and shock hazards.

arrangements of the type described in the above-identified copending application, produce desired output pulses only in response to the discharging of the energy-storage device. By constructing the pulse generator to produce output pulses of a given polarity in response :to the charging as well as the discharging of its energystorage device, very high pulse-repetition frequencies may be obtained It is an object of the present invention, therefore; to provide an improved high-frequency pulse generator in which output pulsesof thesame polarity are derived in response to the charging as well? as the discharging of an energy-storage device.

2 Claims. (Cl. 260-27) It is a further object of the invention to provide an improved high-frequency pulse generator in which output pulses of the same polarity and substantially equal amplitudes are obtained in response to both the charging and discharging of an energy-storage device.

In accordance with the invention, a high-frequency pulse generator comprises means for supplying a unidirectional potential to the generator, having one terminal connected to a common terminal of the generator maintained at a, fixed reference potential and havin a second terminal by-passed for alternating currents to the common terminal. The arrangement has an energy-storage device, including a transmissionline section having an input terminal and havingshunt-connected condensers half of which are connected between the second terminal of the potential-supplying means and the input terminal while the remaining half are connected between the common and input terminals. The generator has means for eiiectively connecting the input terminal to the second terminal of the potential-supplying means to provide a charging circuit for establishing a predetermined charge on the energy-storage device in a time interval which is short with reference to the minimum period of the generated pulses. Additionally, means are provided for effectively connecting the input terminal to the common terminal to provide a discharge circuit for the energy-storage device which is electrically equivalent to its charging circuit. The desired output pulses are obtained through means coupled to the charging and discharging circuits for deriving an output pulse of -a given polarity and amplitude in response to the charging of the energy-storage device and for deriving an output pulse of the same polarity and approximately the same amplitude in response to the discharging of the energy-storage device. Finally, the generator has means for controlling the charging and discharging circuits alternately to charge and discharge the energy-storage device so as to generate output pulses of the above-mentioned given polarity and amplitude and occurring in a predetermined time sequence. I

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a'schematic circuit diagram of a high-frequency pulse generator in accordance with the invention; Fig. 2 is a series of graphs utilized in explaining the operation of the Fig. 1 arrangement; while Fig. 3 i a schematic representation of a portion of the Fig. 1 arrangement in modified form.

Referring now more particularly to Fig. 1 of the drawing, the pulse generator there represented comprises an energy-storage device in the form of an artificial or simulated transmissionline section I having an input terminal H. The line is formed of lumped circuit elements, including series-connected inductors l2, l2 and intermediate shunt condensers I3, l3 arranged to define filter sections. A sufficient number of such filter sections are provided so that the line section l0 in charging and discharging may deliver energy to a load circuit substantially continuously during a desired pulse interval. The line is unterminated at one end and may be considered to be open-circuited.

The generator also comprises a charging circuit for establishing a predetermined charge on line section It! in a time interval which is short with reference to the minimum period of the generated pulses. As here used, the expression period of the generated pulses is intended to define the time interval between corresponding portions of succeeding ones of the generated pulses. This charging circuit is provided by a connection 14 to ground from line section I0 and a resistor IS, a first gas-filled electron-discharge device or tube l6 of the tetrode type, and a first winding section I! of a pulse transformer which serially connect the input terminal I I to a source of unidirectional potential, indicated +3 The potential source is icy-passed to ground for alternating currents by way of a condenser l8 which is large with reference to the line condensers I3.

The line-charging tube I6 is normally maintained in a nonconductive condition. To this end, its control electrode is held at a fixed negative potential with reference to ground by means of a potential source Ec and resistors l9 and connected thereacross in series, while the cathode potential with respect to ground is determined primarily by the charge condition of line section 10. The control electrode of tube I6 is connected to potential source -Ec through the secondary winding of an additional pulse transformer 2|. The screen electrode of this tube is maintained at the potential of its cathode and the control electrode is coupled to its cathode by way of a condenser 22.

There is also provided in the pulse generator 8. discharging circuit for discharging line section II) in a time interval which is short with referenc to the minimum period of the generated pulses. The discharging circuit includes a second gas-filled electron-discharge tube and a second winding section 26 of the first-mentioned pulse transformer which serially connect input terminal H to conductor l4. Discharge tube 25 is similar to the charging tube l6 and is likewise normally maintained in a nonconductive condition. For this purpose, the control electrode of tube 25 is connected to an adjustable tap of a variable resistor 30 included in a biasing circuit consisting of potential source -Ec, variable resistor 30, and resistors 3|, 32, and 33.

A third winding section 21 of the first-mentioned pulse transformer provides means in the generator, coupled to the described charging and discharging circuits, for deriving output pulses in response to both the charging and discharging of line section I0. Winding sections I1 and 26 are so poled that an output pulse of a given polarity is induced in winding 2! in response to the chargin of the line section, while an output pulse of the same polarity is induced in this winding in response to the discharging of the line section, A suitable utilizin circuit may be coupled to the terminals associated with winding 21 for utilizing the output pulses supplied by the generator. Preferably, the load circuit of transformer i1, 25, and 21 is so arranged that, when either charging tube IE or discharging tube 25 is rendered conductive, the impedance coupled to the input terminal of line section I0 corresponds to its characteristic impedance. This proportioning of the r load circuit of the transformer assures maximum power transfer from the generator.

The generator additionally includes means for controlling the described charging and discharging circuits alternately to charge and discharge the line section l0 so as to generate output pulses of a given polarity and occurring in a predetermined time sequence. Where, as in the embodiment under consideration, the charging and discharging circuits individually include electrondischarge tubes normally maintained in a nonconductive condition, the instant means is utilized alternately to render the tubes conductive. The time sequence in which the tubes are rendered conductive determines the time sequence or repetition frequency of the generated pulses. The control means, as illustrated, i provided by an input terminal 40 to which may be applied a control signal for application to the control electrodes of tubes l6 and 25. Terminal 40 is coupled by means of a condenser 4| and leak resistor 42 to the input circuit of a cathode follower, including a triode Vacuum tube 43. The cathode impedance of tube 43 consists of a self-biasing resistor 44 in series with a resistor 45. An amplifier, including a triode 46, is cathode-coupled to cathode follower 43 and includes in its output circuit the primary winding of pulse transformer 2|. The control electrode of charging tube !6 is coupled to the control circuit by way of this pulse transformer. The control electrode of discharging tube 25, however, is coupled through a condenser 41 to the output circuit of amplifier 46. lA voltage divider 48 is utilized in establishing a bias potential on the control electrode of tube 46 and condenser 49 is employed as a blocking condenser. The described control circuit, in conjunction with the potential source -Ec associated with the control electrodes of tubes l6 and 25, serves to control the charging and discharging circuits in a manner presently to be described.

In considering the operation of the pulse generator, it will be assumed initially that line section I!) is completely discharged. For this condition, the cathode of charging tube I6 is at substantially ground potential and the negative potential applied to its control electrode from source 'Ec causes this tube to be nonconductive. Likewise, the discharging tube 25 is nonconductive due to the bias on its control electrode which is selected through adjustment of variable resistor 30 to be much larger than the negative potential on the control electrode of tube l6. It will be assumed, further, that a control signal of the type represented by curve A of Fig. 2 is applied to control terminal 40 from a signal source, not shown in the drawing. The control pulses are translated through cathode follower 43 and amplifier 46 and are applied with positive polarity to the control electrodes of charging tube l6 and discharging tube 25. The first pulse of the applied control signal initiates an electron discharge in tube [6 but is unable to overcome the bias potential on tube 25 which remains nonconductive.

. With tube I conductive, the charging circuit of line section I0 is energized. Transformer windin s I1 and 21 effectively apply an impedance'to the input terminals of line section I 0 which is equal to its characteristic impedance and the potential at the input terminals of the line immediately rises to approximately half the value of source +B. After a predetermined pulse interval, described hereinafter, the line becomes fully charged and the potential level of its input terminals is then approximately equal to that of source +B. Consequently, the cathode potential of charging tube l6 and the anode potential of discharging tube 25 are raised a corresponding amount, biasing tube 16 once again to its non conductive state and reducing the bias level of tube 25 to condition the latter to respond to the next pulse of the control signal.

The described potential variations at the input terminals of line section Hi, the cathode of tube l6, and the anode of tube 25, respectively, are represented by those portions of curves B, C, and D of Fig. 2 which are included within ordinate lines t1 and t2, where h is the instant at which the first pulse of the control signal is applied and 232 is the instant when the line has become fully charged. The charging current which flows in the pulse interval t1-t2 induces an output pulse of a given polarity in transformer winding 21 for application to a utilizing circuit coupled thereto. The output pulse thus obtained in response to the charging of line section I0 is represented by pulse Pi. in curve E of Fig. 2. Its duration is approximately equal to ZVLC, where L and C, respectively, are the total inductance and total capacitance of the line section. During th pulse interval t1- tz,'charging tube I6 is conductive and the step portion S1 of curve C shows its cathode potentialto be equal to the source +B minus the potential drop of its anode-cathode circuit.

When the next succeeding pulse of the control signal is translated through tubes 43 and 4 6 to the control electrodes of tubes I6 and 25, the positive potential of the cathode of tube 16 causes this tube to remain in its nonconductive. state but, in view of the reduced bias on tube 25, the

latter is rendered conductive. With tube 25 conductive, the discharging circuit of line section In is energized and the potential at the input t minals of the line is immediately reduced from its value of source +3 to approximately half that value. After a given pulse interval, determined by the inductance and capacitance of the line, the line becomes completely discharged, retuming its input terminals to ground or zero potential. The cathode of charging tube l6 and the anode of discharging tube 25 are likewise brought to ground potential, conditioning tube I6 to respond to the next pulse of the control signal and biasing tube 25 to its initial, nonconductive state. The described potential changes which accompany the discharge of line section H] are represented by those portions of curves B, C, and D included between the ordinate lines is and 114, where is is the instant at which the second pulse of the control signal occurs and t4 is the instant when the line is completely discharged. Current flow through the transformer winding 26 in the discharging of the line section induces in winding 21 a second output pulse. This pulse ob- "tained in response to the discharging of the line section is represented at Pa of curv E and has the same polarity and duration as the preceding pulse P6,, resulting from the line charging process. The step portion S: of curve D designates the potential drop in the anode-cathode circuit of tube 25 during the pulse interval ta-tr in which this tube is conductive.

The remaining control signals of curve A repeat the described cycle of operation in which the line section is first charged to derive an output pulse and then discharged to derive the succeeding output pulse. Curve E represents the time sequence of the generated pulses which will be seen to correspond with that of the applied control pulses. In selecting the control signal, it is necessary that the time separation between succeeding pulses thereof be more than the deionization interval of charging tube l6 and discharging tube 25. In other words, while these tubes are rendered conductive in alternation, neither is rendered conductive until the deionization interval of the other has passed. It will be clear that if tube 25, for example, were triggered during the deionization interval of tube IS, a lowimpedance-path would be established across potential source +B. This undesired result is obviated by spacing the pulses of the control signal in the manner mentioned above. I

The generator of Fig. l is effective to produce output pulses of high repetition frequencies, limited only by the deionization intervals of tubes I6 and 25. The maximum repetition frequency is obtained when these tubes are so controlled that each is rendered conductive immediately following the deionization interval of the other. In addition to providing pulses of high repetition frequencies, the generator has the advantage of high efliciency. This follows from the fact that the energy available in both the charging and discharging process is utilized in deriving output pulses.

The wave forms of the curves of Fig. 2 have been idealized to simplify the description. As a practical matter, the pulses obtained in the charging process have a smaller amplitude than those resulting from the discharging process. This is due to the dissimilarity of the charging and discharging circuits. In this connection, it will be noted that the discharging circuit ineludes only the line section I 0, winding 26 and discharging tube 25, while the impedance elements involved in the charging process are the line section l0, winding I1, charging tube l6, and by-pass condenser l8. Where the charging and discharging circuits are electrically equivalent to one another, the output pulses have the same amplitude as well as the same polarity. l Fig. 3 represents a modification of the charging and discharging circuits of the Fig. I arrangement with which output pulses of equal amplitudes are obtained. The components of Fig. 3 which correspond to those of Fig. 1 are identified by the same reference characters. As in the Fig. 1 arrangement, one terminal 60 to which source +B is applied is connected to a common terminal that is maintained at a fixed reference potential,

specifically ground, while the alternate terminal circuit arrangement is identical with the corresponding portion of Fig. 1 and may be controlled by the same type of control circuit to generate output pulses. The control circuit, however, has been omitted to simplify the drawing.

In considering the operation of the Fig. 3 embodiment, assume that tubes i6 and 25 are in their normal, nonconductive states. By-pass condenser IB. is charged from source +3 and the line condensers 50, 5!] and 5|, 5| form a capacitivetype voltage divider coupled across by-pass condenser IB. The line condensers then acquire identical charges, individually equal to half the value of the source +B. If charging tube I6 is triggered, a short circuit is effectively established across line condensers 5|], 50 so that the alternate condensers 5|, 5| receive a'charge equal to source +B and condensers 5|), 5|! are dis charged. The current flow through the network in this process provides one output pulse of a given polarity and amplitude. If now, discharging tube 25 is rendered conductive, a short circult is effectively established across condensers 5|, 5| which discharge and supply a second output pulse while condensers 50, 59 become fully charged. The circuit is now conditioned to generate a third pulse in response to the triggering of tube I6 and the charging of condensers 5|, 5|. Thus, in the Fig. 3 arrangement, condensers 5|, 5! constitute the energy-storage device which is alternately charged and discharged to generate output pulses. The pulses obtained thereby are of the same polarity and equal am plitude since in each operation half of the line condensers are charged to the potential level of source +B while the other half become discharged, and since identical impedances are involved in each case.

In each of the described embodiments of the invention, gas-filled tubes are employed in the charging and discharging circuits in order that their high current-carrying capacity may be exploited to generate output pulses of high power. If desired, vacuum tubes may be utilized in their stead in which case no deionization phenomenon is involved and increased repetition frequencies limited only by tube dissipation capabilities are possible.

Pulse generators constructed in accordance with the teachings of this invention are subject to a variety of applications. In the communication field, for example, they may be used to pulse-modulate a transmitted carrier-wave signal. In industrial fields they may be included in welding systems and the like.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A high-irequency pulse generator comprising, means for supplying a unidirectional potential to said generator having one terminal connected to a common terminal of said generator maintained at a fixed reference potential and having a second terminal by-passed foralternating currents to said common terminal, an energystorage device including a transmissiondine section having an input terminal and having shuntconnected condensers half of which are connected between said second terminal of said potential supplying means and said input terminal while the remaining half thereof are connected between said common terminal and said input terminal, means for eiiectively connecting said input terminal to said second terminal -of said potential supplying means to provide a charging circuit for establishing a predetermined charge on said energy-storage device in a time interval which is short with reference to the minimum period of the generated pulses, means for effectively connecting said input terminal to said common terminal to provide a discharging circuit for said energy-storage device which is electrically equivalent to said charging circuit, means coupled to said charging and discharging circuits for deriving an output pulse of a given polarity and amplitude in response to the charging of said energy-storage device and for deriving an output pulse of the same polarity and approximately the same amplitude in response to the discharging of said energy-storage device, and means for controlling said charging and discharging circuits alternately to charge and discharge said energy-storage device so as to generate output pulses of said given polarity and amplitude and occurring in a predetermined time sequence.

2. A high-frequency pulse generator comprising, means for supplying a unidirectional potential to said generator having one terminal grounded and having a second terminal bypassed for alternating currents to ground, an energy-storage device including a transmissionline section having an input terminal and having shunt-connected condensers half of which are connected between said second terminal of said potential supplying means and said input terminal while the remaining half thereof are connected between ground and said input terminal, means for effectively connecting said input terminal to said second terminal of said potential supplying means to provide a charging circuit for establishing a predetermined charge on said energy-storage device in a time interval which is short with reference to the minimum period of the generated pulses, means for effectively connecting said input terminal to ground to provide a discharging circuit for said energy-storage device which is electrically equivalent to said charging circuit, means coupled to said charging and discharging circuits for deriving an output pulse of a given polarity and amplitude in response to the charging of said energy-storage device and for deriving an output pulse of the same'polarity and approximately the same amplitude in response to the discharging of said energy-storage device, and means for controlling said charging and discharging circuits alternately to charge and discharge said energy-storage device so as to generate output pulses of said given polarity and amplitude and occurring in a predetermined time sequence.

JOHN A. RADO. 

